1. Field of the Invention
The present invention relates to a thin film transistor substrate and a fabrication method therefor, and more particularly, to an organic thin film transistor substrate capable of simplifying a process and improving picture quality, and a fabrication method therefor.
2. Description of the Related Art
A liquid crystal display (LCD) device displays images by controlling the light transmittance of liquid crystals having dielectric anisotropy using an electric field. The LCD device includes an LCD panel for displaying images through a liquid crystal cell matrix and driving circuits for driving the LCD panel.
The LCD device displays images by causing each of liquid crystal cells arranged in a matrix form in the LCD panel to control the light transmittance according to a video signal.
A thin film transistor (TFT) is used as a switching element for independently supplying the video signal to each of the liquid crystal cells. Amorphous silicon or polycrystalline silicon is used as an active layer of such TFT.
However, since the amorphous silicon or polycrystalline silicon active layer is patterned through a thin film depositing (or coating) process, a photolithography process and an etching process, the fabricating process becomes complicated and expensive. Therefore, it has been proposed to form organic TFT using an organic semiconductor layer which can be formed through a printing process.
The organic semiconductor layer of the organic TFT is protected by a passivation layer formed within a hole provided by a bank insulating layer. However, because the passivation layer differs in thickness between the edge and center within the hole the passivation layer looks like a stain. In addition, moisture and chemical liquid permeate into the boundary between the passivation layer and the organic semiconductor layer, thereby damaging the organic semiconductor layer. Moreover, in a conventional organic TFT substrate, since a bank insulating layer having a hole filled with the passivation layer and a bank insulating layer having a hole filled with the organic semiconductor layer are formed by separate mask processes, a fabricating process is complicated.